Thin films of silicon nitride have been widely used in various applications due to their unique physical, chemical and mechanical properties. In semiconductor devices particularly, silicon nitride films are used as gate insulations, diffusion masks, sidewall spacers, passivation and encapsulation, etc. Typically, silicon nitride films used in the Front End of Line (FEOL) are currently deposited by Low pressure chemical vapor deposition (LPCVD) in a hot wall reactor at >750° C. using dichlorosilane and ammonia. As the lateral and vertical dimensions of Integrate Circuit (IC) continue to shrink, however, there is an increasing demand for silicon nitride films to be deposited at much lower temperatures (<550° C.) in order to avoid unwanted reaction between Si and metal, and realize ultra-high integration devices with precise doping profile control.
To grow silicon nitride films at low temperatures, recently, there have been reports that the addition of small amount Ge may lead to the reduction of required deposition temperature for silicon nitride films (U.S. Pat. No. 7,119,016 B2). But this may introduce unwanted impurity to the film, causing reliability issues for the devices that the film is suited for, and may also increase the complexity of the deposition process and cost.
Recent innovations to improve complementary metal oxide semiconductor (CMOS) transistor performance have created an industry need for strained ceramic layers compatible with current ultra-large scale integration (ULSI) techniques. In particular, channel carrier mobility for negative metal oxide semiconductor (NMOS) transistors can be increased through introduction of tensile uniaxial or biaxial strain on a channel region of the MOS transistor. Similarly, compressively strained films can be used to realize an enhancement in channel carrier mobility for positive metal oxide semiconductor (PMOS) transistors. In US Publication 2008/0081470A1, a method for forming a strained SiN film and a semiconductor device containing the strained SiN film is disclosed.